A racer protects his lungs as he bares his chest in the 3.5k Undies Run at Olympic Park in Beijing. In January, Beijing scored a 755 on the EPA's Air Quality Index, a 500-point scale in which 150 is "unhealthy" and above 300 is "hazardous."

from the Usiazha River on a frigid day near the Belarus village of Usiazha.

Steam rises

from the Usiazha River on a frigid day near the Belarus village of Usiazha.

Photo: Viktor Drachev, AFP/Getty Images

Steam rises from the Usiazha River on a frigid day near the... Photo-4253287.57474 - SFGate

Image 12 of 20

Leave them alone and they'll come home …

and stand at the barn bleating until you let them in out of the snow. (Basque village in Oquendo, Spain.)

Leave them alone and they'll come home …

and stand at the barn bleating until you let them in out of the snow. (Basque village in Oquendo, Spain.)

Photo: Rafa Rivas, AFP/Getty Images

Leave them alone and they'll come home … and stand at the... Photo-4253267.57474 - SFGate

Image 13 of 20

Kansas gets socked again:

With the temperature barely above freezing, snowflakes turn to water droplets on a car window in Hutchinson, Kan. The latest Midwest storm was expected to dump between eight and 24 inches of snow on the area.

Joe Hanson, a Vietnam veteran who suffers from post traumatic stress disorder, says his service dogs Star and Kira help keep him calm. He takes them everywhere on his motorcycle, including to the VA hospital in Gainesville, Fla., where he had an appointment Monday.